A conventional image forming apparatus includes an image carrier, such as a photosensitive drum, on the surface of which an electrostatic image is formed. The image forming apparatus further includes a developing roller developing the electrostatic latent image by sticking toner on the surface of the image carrier and forms an image by transferring the toner stuck on the surface of the image carrier by the developing roller onto a recording medium. In this type of image forming apparatus, the electrostatic latent image is developed by sticking toner on the surface of the image carrier bearing the electrostatic latent image using the developing roller. The image corresponding to the electrostatic latent image is formed on the recording medium by transferring the stuck toner onto the recording medium.
In this type of image forming apparatus, various processing devices including a charger that uniformly charges the image carrier before the electrostatic latent image is formed on the surface of the image carrier by exposing and a transfer roller that transfers toner stuck on the surface of the image carrier onto the recording medium are provided around the image carrier. Voltage acting between the processing device or the above-mentioned developing roller and the image carrier may be applied (e.g. see JP-A-11-327288).
In the image forming apparatus, the charger and the developing roller are accommodated in a cartridge and detachable from the image carrier. The components are replaceable according to each life span. JP-A-11-184195 discloses an image forming apparatus in which voltage is applied to a developing unit accommodating a developing roller through a charging unit accommodating a charger.